Subject: Re: [bitcoin-dev] BIP Proposals for Output Script Descriptors

From: Daniel Bayerdorffer <[email-masked]>
Date: Sun, 4 Jul 2021 13:56:28 -0400 (EDT)

Hello, 

I just wanted to put my two cents in, on the metal backup aspect. We make the Bitcoin Recovery Tag for a similar purpose. We use a fixed font, so using ' (apostrophe) or H/h are both acceptable. Most metal stamping tools are fixed width fonts. 

You can see a picture here... 
[ https://cyphersafe.io/product/bitcoin-recovery-tag/ | https://cyphersafe.io/product/bitcoin-recovery-tag/ ] 

Thanks, 
Daniel 

-- 
Daniel Bayerdorffer, VP [email-masked] 
Numberall Stamp & Tool Co., Inc. www.numberall.com 
Reuleaux Models www.reuleauxmodels.com 
CypherSafe www.cyphersafe.io 
PO BOX 187, Sangerville, ME 04479 USA 
TEL: 207-876-3541 FAX: 207-876-3566 

From: "Craig Raw via bitcoin-dev" <[email-masked]> 
To: "David A. Harding" <[email-masked]> 
Cc: "Bitcoin Protocol Discussion" <[email-masked]> 
Sent: Saturday, July 3, 2021 10:00:51 AM 
Subject: Re: [bitcoin-dev] BIP Proposals for Output Script Descriptors 

It's a consideration, not a serious concern. 
When I made the point around alphanumeric characters being similar to the path numbers, I was actually thinking of the output descriptor appearing in a fixed character width font, which I prefer as more appropriate for displaying hexidecimal values. In this case, the apostrophe provides more whitespace which makes the path easier to parse visually. It's difficult to reduce this to a mathematical argument, as is true for many UX considerations. Your example in fixed width here: [ https://gist.github.com/craigraw/fc98b9031a7e01e1bc5d75a77bdb72e5 | https://gist.github.com/craigraw/fc98b9031a7e01e1bc5d75a77bdb72e5 ] 

That said you make good arguments around the shell quoting and stamps for metal backups, and therefore I agree it is preferable to use the lowercase "h". Thanks for the detailed reply. 

Craig 

On Sat, Jul 3, 2021 at 12:11 PM David A. Harding < [ mailto:[email-masked] | [email-masked] ] > wrote: 

On Sat, Jul 03, 2021 at 10:35:48AM +0200, Craig Raw wrote: 
> There is a downside to using "h"/"H" from a UX perspective - taking up more 
> space 

Is this a serious concern of yours? An apostrophe is 1/2 en; an "h" is 
1 en; the following descriptor contains three hardened derivations in 149 
characters; assuming the average non-'/h character width is 1.5 en, the 
difference between 207 en and 208.5 en is barely more than half a 
percent. 

pkh([d34db33f/44h/0h/0h]xpub6ERApfZwUNrhLCkDtcHTcxd75RbzS1ed54G1LkBUHQVHQKqhMkhgbmJbZRkrgZw4koxb5JaHWkY4ALHY2grBGRjaDMzQLcgJvLJuZZvRcEL/1/*)#ml40v0wf 

Here's a direct visual comparison: [ https://gist.github.com/harding/2fbbf2bfdce04c3e4110082f03ae3c80 | https://gist.github.com/harding/2fbbf2bfdce04c3e4110082f03ae3c80 ] 

> appearing as alphanumeric characters similar to the path numbers 

First, I think you'd have to be using an awful font to confuse "h" with 
any arabic numeral. Second, avoiding transcription errors is exactly 
why descriptors now have checksums. 

> they make derivation paths and descriptors more difficult to read. 

The example descriptor pasted above looks equally (un)readable to me 
whether it uses ' or h. 

> Also, although not as important, less efficient when making metal 
> backups. 

I think many metal backup schemes are using stamps or punch grids that 
are fixed-width in nature, so there's no difference either way. (And 
you can argue that h is better since it's part of both the base58check 
and bech32 character sets, so you already need a stamp or a grid row for 
it---but ' is otherwise unused, so a stamp or grid row for it would be 
special). 

But even if people are manually etching descriptors into metal, we're 
back to the original point where we're looking at something like a 0.7% 
difference in "efficiency". 

By comparison, the Bitcoin Core issue I cited in my earlier post 
contains several examples of actual users needing technical support 
because they tried to use '-containing descriptors in a bourne-style 
shell. (And I've personally lost time to that class of problems.) In 
the worst case, a shell-quoting accident can cause loss of money by 
sending bitcoins to the descriptor for a key your hardware signing 
device won't sign for. I think these problems are much more serious 
than using a tiny bit of extra space in a GUI or on a physical backup 
medium. 

-Dave 

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